AngularJs中的类操作和实例操作有什么区别？

关于类vs实例的事情是关于它为了方便使用而做的事情. “类操作”是指从您自己创建的资源类调用操作,有点像其他语言中的静态或共享方法.当您还没有实例时,这可用作获取,查询或保存资源实例的入口点.获取和查询是最明显的例子.如果您有汽车资源,并且需要检索它,那么您从哪里开始？当然,有了集体诉讼,比如获得.

现在,当您的资源类检索现有实例,或者您创建一个新实例时,$resource将使用为您的资源定义的操作扩展您的实例,但前缀为$,因此它们不会与您资源上的字段发生冲突.这些是您的实例操作.实例和类之间的区别是实例是在当前实例的上下文中完成的.因此,如果您获得一个实例,然后在该实例上调用$save或$delete,它将专门保存或删除该实例.实例操作只是为了方便起见.

所以它们几乎相同,不同之处在于它们的使用环境.

function($resource) {     

   // first let's define a new resource for car,where all cars have an id field
   // calling $resource will create a new resource class that can be used to 
   // create,retrieve,update,or delete instances
   // this is usually done as a service and injected into controllers as needed.
   var Car = $resource('/api/car/:id',{id: '@id'});

   // the car class we just created has some class actions that can help you query for or get car instances
   // let's create a new instance of a car and save it
   var newCar = new Car({make: 'Toyota',model: 'Prius'});
   // the prototype of Car includes the instance action versions of the actions defined for the resource. below,$save is your instance action
   newCar.$save(); // server will respond with the object after it's saved,so we can now access the id. let's say the id it returned is 24,we'll reference this value later.


   // now,let's imagine some time later we want to retrieve the car and update it
   // Car.get is a class action that requests the resource from the server,parses the JSON into an object,and merges it with the Car instance prototype so you have your instance actions
   // let's get the car we created previously.
   // remember,this is done asynchronously,so we will do our work in a success handler that we provide to get
   Car.get({id: 24},function(myCar) {
       // let's update the car now that we have it. let's set the year of the model and the color
       myCar.year = 2004;
       myCar.color = 'white';

       // now,let's save our changes by calling the instance action $save
       myCar.$save();
   });


   // now,let's query for all cars and get an array back
   // query is a class function that expects an array of your resource to be returned
   Car.query(function(cars) {
        // trivial example,we're just going to enumerate the cars we found and log some info about them
       for(var i = 0; i < cars.length; i++)
          console.log('Found ' + cars[0].color + ' ' cars[0].year + ' ' + cars[0].make + ' ' + cars[0].model);
   });


   // ok,let's delete the car we created earlier. use the class action delete
   Car.delete({id: 24});
}

从技术上讲,您可以将任何操作调用为类或实例,但很明显,有些操作很难用作实例操作,反之亦然.例如,虽然你在技术上可以使用查询作为实例动作,但你不会在实践中这样做,因为它是额外的工作而且很尴尬(你必须做新的Car().$query().这太傻了. .query()更容易,更有意义).因此,上面示例中的用法表示您的正常用法.

更新：

保存vs $save

$save与save类似,但它假设您要在save期间提交的数据本身,因为$save是一个实例操作.它特别有用,因为在收到响应后,它将使用HTTP端点返回的对象更新自身.因此,如果您的服务使用服务器端填充的一些其他值(例如ID)保存对象,然后将对象作为JSON发回,$save将使用返回的JSON对象更新实例.

var car = new Car({make: 'Toyota',model: 'Prius'});
 // at this point there is no id property,only make and model
 car.$save(function() {
    // angular is async,so we need a success handler to continue the explanation

    // assuming your server assigned an ID and sent the resulting object back as JSON,you can now access id off the original object
    console.log(car.id); // has a value now
 });

您可以使用类方法执行类似的操作,但它很笨拙,特别是如果您正在处理它时控制器中的其他代码需要引用汽车

Car.save({make: 'Toyota',model: 'Prius'},function(car) {
       // ok,we have an ID now
       console.log(car.id);
 });

要么

var car = new Car({...});
 Car.save(car,function(newCar) {
      car = newCar; // wut? that's awkward
 });

在快速保存小对象或执行某种“火灾和忘记”的情况下,保存可能很有用.无论如何,我很少使用保存自己.